According to an existing color cathode-ray tube (CRT), electrons emitted from an electron gun partly collide against the inside wall of a neck or ions ionized by the emitted electrons adhere to it, and electrification is caused. Therefore, an antistatic film is formed on a glass substrate of the inside wall of the neck in order to prevent the track of the emitted electrons from being deflected by the electrification and their arrival to a proper position on a phosphor layer from being disturbed.
As a material for forming of such an antistatic film, there have been used fine particles comprised of a semiconducting substance having a specific resistivity of 105 Ω·cm or more, such as an ITO (Indium-Tin-Oxide), an ATO (Antimony-Tin-Oxide) or ZnO2.
There is also a generally known method of adding a surface active agent or quaternary amine to SiO2 or applying it to an SiO2 film so to form a film having ion conductivity.
However, any of the films was not satisfactory enough as an antistatic film to be disposed on an insulating member arranged in a vacuum envelope, such as the inside wall of the neck of a color cathode-ray tube.
Specifically, the antistatic film including fine particles comprised of the semiconducting substance such as an ITO or an ATO has a high dependency of a resistance value (surface resistivity) on the thickness of the film, and it was necessary to control quite accurately the thickness of the film in order to control the surface resistivity in the most desirable range of 1010 to 1012 Ω/cm2. And, because methods such as spray coating and brushing are hard to accurately control the thickness of the antistatic film, these methods could not be used, and a dip coating method or a spin coating method involving a high production cost was used to form the antistatic film. Even when the dipping method or the spin coating method is used, it was necessary to strictly control the thickness of a film, and there were disadvantages that the control of the film thickness was troublesome and the production cost was high.
Since an existing film having ion conductivity has a reduced dependency of a resistance value on the thickness of a film but a large dependency on environments, such as a temperature and a humidity, and poor reliability, it could not be used as an antistatic film for the interior of a vacuum tube or the like in particular.
The present invention was achieved in order to remedy the above problems, and it is an object of the invention to provide an antistatic film having stable antistatic properties because it has a reduced dependency of a resistance value on the thickness of the film and a reduced dependency on environments such as a temperature and a humidity, a dispersion which allows to form such an antistatic film by a simple and easy applying method, and an image display device having the antistatic film.